Navigation Errors

[Don33]

Lexi Fans, I have a very basic knowledge of how the GPS works but not much more. Yesterday the Nav was working fine as usual until I noticed that the position marker showed me about a mile or two east of where I actually was. I also noticed that the GPS indicator was not on. Now that I have begun to watch for it, it is off most of the time but the map is typically spot on. Is this normal? BTW I don’t have any of the widows tinted. Your thoughts?

[curiousB]

nav_diag_modes.pdf

NAV_diag_entry_mode.pdf

Most satellite navigation systems use a few factors to determine where you are on the map. The main input is the GPS position as derived from the satellite receiver in your car. In addition to that there are inputs from the wheels (odometer) and compass heading which also factor into your position. The idea is if you temporarily are blocked from satellites the system can still keep you updated by you incrementally following the map using your heading and distance travelled.

If your GPS receiver isn’t working then this method of keeping track of position eventually loses accuracy as it needs periodic GPS locations to keep it straight.

So you need to find out why the GPS receiver isn’t working properly. The antenna for it is on the top of the dash right under the rear view mirror (you can’t see it it is underneath the dash cover. You don’t have a cookie sheet sitting there blocking the antenna do you? :D

There is a dealer/factory test mode you can put your nav system into that shows a bunch of technical stats of the GPS receiver (# satellites seen, signal strength and so on, maybe search this forum for the keypad sequence to jump into this mode. Its pretty technical though and probably won’t tell you much more than if you are seeing satellites or not).

Attached are a couple of PDFs to show you how to get into factory mode and what screens you have. Be careful if you change some things you could create big time problems. If you don’t know what it is don’t change it.

[Don33]

nav_diag_modes.pdf

NAV_diag_entry_mode.pdf

Most satellite navigation systems use a few factors to determine where you are on the map. The main input is the GPS position as derived from the satellite receiver in your car. In addition to that there are inputs from the wheels (odometer) and compass heading which also factor into your position. The idea is if you temporarily are blocked from satellites the system can still keep you updated by you incrementally following the map using your heading and distance travelled.

If your GPS receiver isn’t working then this method of keeping track of position eventually loses accuracy as it needs periodic GPS locations to keep it straight.

So you need to find out why the GPS receiver isn’t working properly. The antenna for it is on the top of the dash right under the rear view mirror (you can’t see it it is underneath the dash cover. You don’t have a cookie sheet sitting there blocking the antenna do you? :D

There is a dealer/factory test mode you can put your nav system into that shows a bunch of technical stats of the GPS receiver (# satellites seen, signal strength and so on, maybe search this forum for the keypad sequence to jump into this mode. Its pretty technical though and probably won’t tell you much more than if you are seeing satellites or not).

Attached are a couple of PDFs to show you how to get into factory mode and what screens you have. Be careful if you change some things you could create big time problems. If you don’t know what it is don’t change it.

[Don33]

Thanks for the info. I viewed the screens and discovered that the NAV can track 8 sats. It shows that it receives information from only seven and uses data from only 4 at a time. The error message log shows many entries. At this moment, it is tracking zero sats. I guess it’s time to see the dealer…it’s out of warranty at the end of October.

[curiousB]

The satellites are in constant orbit around the earth so the GPS is always dropping one satellite off and picking up another coming round the bend. It can give position with as little as one but it gets more accurate with more points of reference.

Good to hear its on warranty as I doubt the dealer can do much other than swap the entire receiver module. I'm sure that is a pricey affair given its a Lexus.

[Don33]

The satellites are in constant orbit around the earth so the GPS is always dropping one satellite off and picking up another coming round the bend. It can give position with as little as one but it gets more accurate with more points of reference.

Good to hear its on warranty as I doubt the dealer can do much other than swap the entire receiver module. I'm sure that is a pricey affair given its a Lexus.

There is just one other thing that I'm curious about...I installed a VAIS Tech iPOD adapter about a year ago. I'm wondering if it can give off any signals that would disrupt the nav. I left them a message at their tech support and am now awaiting an answer. Thanks again.

[curiousB]

I doubt it. All electronic devices radiate unwanted signals due to the nature of switching transistors in circuits. The FCC regulates these emissions to be under certain thresholds to not interfere with radio and TV signals. GPS uses a very high frequency of 1.57542GHz and 1.2276GHz for the receivers so at this higher end any stray radiation from other electronics would be very low. Furthermore GPS uses a spread spectrum technique that allows it to discern between multiple signals on the same frequency.

Bottom line the only way this iPOD add on impacted the GPS is if they erroneously cut a wire for the receiver during install or your iPOD dock is placed on top of the antenna.